Diagnostic and interfacial pad for use with the socket of a prosthetic device

ABSTRACT

An interfacial pad adapted to be inserted between a prosthetic device and a body member is provided comprising a relatively low density, substantially non-resilient, deformable foam pad exhibiting a cushioning characteristic and a memory characteristic responsive to locally applied forces.

United States Patent [191 Pollack [54} DIAGNOSTIC AND INTERFACIAL PAD FOR USE WITH THE SOCKET OF A PROSTHETIC DEVICE H [75] Inventor: Herman G. Pollack, West Hartford,

Conn.

[73] Assignee: Elliott S. Pollack, Bloomfield, Conn.,

part interest each [22] Filed: Mar. 1,1971

[21] Appl. No.: 119,751

[52] 11.8. C1. ..3/l9, 128/2 S, 260/2.5 AK,

260/25 L, 264/222, 264/D1G. 3O [51] Int. Cl. ..A61f 1/02, A61b 5/10 [58] Field 01' Search ..3/17-20;

128/594, 595, 2 S, 586; 36/71; 264/D1G. 30, 222, 223, 50, 321; 260/25 L, 2.5 AK

[56] References Cited UNITED STATES PATENTS 3,253,600 5/1966 Scholl 1 28/594 X 3,548,420 12/1970 Spence ..3/20

[111 3,732,578 [4 1 May 15,1973

OTHER PUBLICATIONS The Interface in the Immediate Pos tsurgical Prosthesis by J. H. Zettl, Orthotics & Prosthetics, Vol. 24, No. 1, March 1970, pp. 1-6.

Primary Examiner-Richard A. Gaudet Assistant Examiner-Ronald L. Frinks Attorney-William Kaufman and Barry Kramer [57] ABSTRACT An interfacial pad adapted to be inserted between a prosthetic device and a body member is provided comprising a relatively low density, substantially nonresilient, deformable foam pad exhibiting a cushioning characteristic and a memory characteristic responsive to locally applied forces.

8 Claims, 3 Drawing Figures Pmm'rm 2m 1 5m INVENTOR. 12 P0 ZZac/F/ Herma ATTORNEYS DIAGNOSTIC AND INTERFACIAL PAD FOR USE WITH THESOCKET OF A PROSTHETIC DEVICE This invention relates to improvements in prosthetic devices. The invention relates more particularly to an improved method and means for providing a conforming fit between a distal portion of a body member and a prosthetic device.

A principal requirement in fitting a prosthetic device such as an artifical limb to a human body member is the comfort of the user. At times the interface established between the human body member and the prosthesis while substantially conforming to the shape of the distal portion of the member will result in severe discomfort. This is particularly true when the body member supports a significant loading. This situation frequently occurs with a below the knee amputee, for example, when a distal bony segment of a leg member is irregular and even jagged. These irregular or jagged segments, which can be visibly hidden, establish pressure points at the interface. Although resilient cushioning devices have been suggested as an interface medium and therefore alleviate the discomfort to some extent, the pressure points created by bone irregularities will continue to cause discomfort unless the thickness of the interface material is made undesirably large. Such an arrangement would seriously hamper the desired total contact of the body member with the socket of the prosthetic device.

Accordingly, it is an object of this invention to provide an improved interface between a body member and a mating prosthetic device.

Another object of the invention is the provision of an improved cushioning interface means for a prosthetic device.

Another object of the invention is the provision of a cushioning interface for inhibiting discomfort which can arise from pressure points existing at an irregular bone surface at a distal segment of a body member.

A further object of the invention is the provision of a method for detecting and correcting for these pressure points.

In accordance with the general features of this invention, a conforming interface between a prosthetic device and a body member is provided comprising a relatively low density deformable pad exhibiting a cushioning characteristic as well as a memory characteristic which is responsive to the local application of a force.

The pad which comprises a relatively low density latex foam having high compression set is adapted to be employed as a removable insert or a permanent laminate for a prosthetic device and provides a cushion which conforms on one surface to a surface of the socket of the prosthetic device and on another surface to the distal segment of a human body member. In accordance with other features of the invention, the pad material exhibits a particular coloration which coloration will vary under the application of force at pressure points and thereby reveal the location and magnitude of otherwise unknown pressure points.

In accordance with the method of the present invention, a prosthetic socket cushion, cup-like in form, is inserted in the socket of a prosthetic device, preferably along the forward wall thereof in the direction of motion. The cushion comprises a low density deformable material having a memory characteristic responsive to locally applied force. The prosthesis is then joined to the human body member and the user is encouraged to mildly exercise under normal conditions. The prosthesis is then removed and the insert is examined. The location of pressure points can thus be readily detected and the interior receptive surfaces of the prosthetic device can be modified accordingly to equalize any existing pressure differentials, thereby substantially alleviating the discomfort caused by such pressure points. If desired, however, modification of the interior surface of the prosthetic device can be eliminated altogether by permanently adhering the insert to the interior surface of the prosthetic device.

These and other objects and features of the invention will become apparent with reference to the following specifications and to the drawings wherein:

FIG. 1 is an isometric illustration of a cup-shaped pad constructed in accordance with the features of the invention;

FIG. 2 illustrates the union of a prosthetic device and a human body member as well as the positioning of a foam interface therebetween constructed in accordance with features of this invention; and

FIG. 3 is a sectional view of the interface pad of FIG. 2 after removal illustrating the pressure points created in the pad and retained therein by the memory effect of the pad.

Referring now to FIG. 1, an interface between a human body member and a prosthetic device is shown to comprise a cup-shaped pad 10 of a relatively low density material which exhibits a cushioning effect as well as a memory effect for locally applied forces. As indicated in greater detail hereinafter, the material from which the pad 10 may be fabricated comprises a latex foam. FIG. 2 illustrates the use of the pad 10 of FIG. 1 as a cushioning insert and interface between the human body member 12 and the prosthetic device 14. The prosthetic device 14 is shown as comprising the lower portion of a leg as, for example, would be suitable for use with a below the knee amputee. Although great skill and care is exercised in conforming the interior receptive surfaces of the prosthetic device to the distal portion of the human body member 12, nonetheless protrusions 16 occur along the distal portion of the human body member which ultimately result in pressure being created at these points by contact with the prosthetic device. The net result for the user is the creation of severe discomfort at these points.

In accordance with a feature of the present invention, a conforming interface is provided comprising a cupshaped pad 10 which is initially inserted in the prosthetic device prior to union of the device and the body member 12. Thereafter, the user employs the device in a normal manner for an initial limited period of time as, for example, at least a few hours, then the prosthetic device 14 and insert 10 are removed. Because of the characteristics of the insert, any pressure points which would otherwise have been created because of the interaction of protrusions 16 with the interior surface of of the prosthesis will instead, have created impressions 18 (FIG. 3) in the support pad 10. These impressions remain in the removed insert as a result of the memory effect of the insert. As shown in FIG. 3, the removed insert which now conforms to the surface configuration of the human body member on one surface 20 thereof and the prosthetic device on another surface 22 thereof is examined to determine the location and magnitude of any variations in thickness along its cross section.

Any variations in thickness within the pad clearly indicate differences in distal pressure. It is considered preferable to then alter the contour of the interior receptive surface of the prosthetic device at those points where pressure is indicated, thereby equalizing the pressure exerted by any bony protrusions, and thus assuring total contact within the socket of the prosthesis and enhanced comfort for the user. Thereafter, if desired, a new pad of the type described herein can be inserted within the prosthetic device, primarily for purposes of cushioning and comfort, but also as a means of checking for uncorrected areas of differential pressure. Thus, in those cases where the pressure points are not significant, the insert functions as a cushioning device and interface between a human body member 12 and the prosthetic device 14. In those instances where the pressure points are significant and the cross sectional area of the insert is insufficient for relieving the discomfort of the user, the original insert acts as a mold which provides distinct indications regarding the location and magnitude of the pressure points of the human body member and from which corrections can be made to the prosthesis to alleviate the discomfort at these points.

As indicated hereinbefore, the insert material forming the interface may comprise a material having a particular coloration which coloration undergoes variation upon .the application of pressures at localized points along its cross section. In this instance then, not only are the depressions 18 in the original insert determinative of the pressure points'created by the distal portion of the body member 12, but the variation in coloration of the interface is also an indication of the location of these points and magnitude of the pressure exerted at any given point. Thus, in accordance with the present invention, the cross section of the cup-shaped pad is substantially immediately modified to provide the greatest degree of total contact between a human body member and the prosthetic device while at the same time providing a desired degree of cushioning at localizedpressure points.

The cup-shaped interfacialpads of the present invention are prepared from polymeric latex foams. Any

polymeric latex can be suitably employed as, for example, latices of natural rubber, styrene-butadiene rubber (SBR), polybutadiene, polyisoprene, neoprene, plasticized poly (vinyl chloride), polyurethanes, nitrile rubbers, polystyrene, polyethylene and the like as well as mixtures thereof. Preferably, a natural rubber or a mixture of a natural rubber and a styrene-butadiene rubber latex is employed.

Generally, the latex foam is prepared by charging the latex into a suitable stirred vessel and adjusting the speed so that mixing is vigorous but vortexing is avoided. Thereupon, a foam stabilizer and curing ingredients such as vulcanizing agents and organic accelerators are added. The resulting mixture is stirred until all ingredients are-thoroughly dispersed. The mixture can then be allow'edto mature or age for from about 16 to about20 hours at 75 F to about 100F. If desired, however, the aging period can be eliminated and the above components can be thoroughly admixed together immediately prior to use.

After the aging period is completed or when it is desired to form the foam, the mixture is again subjected to vigorous (but not violent) agitation and antioxidants,

[pigments or dyes, a tackifying'resin and any additional foam stabilizer that may be required is added. The re sulting mixture is stirred until a thorough dispersion is obtained. The resulting mixture is then transferred to a high speed mixing vessel and whipped at high speed until a volume increase of at least about 10 times is obtained. At this point, the cure activator is added and thoroughly dispersed followed by the gelling agent. Once all of the ingredients are thoroughly dispersed in the foam, the foam can be poured into the molds. The molds are then capped with an inverted conical-shaped cap to form the cup-shaped pads of the present invention. After the foam has gelled within the molds, it is considered preferably to allow it to set for about 10 minutes or until the soap structure has been substantially destroyed by further action of the gelling agent. Thereafter, the caps are removed from the molds and the foam cups are stripped therefrom and placed on racks to be air dried under ambient conditions for about 36 to about 48 hours. It has been found in accordance with the present invention that the foam cups must be cured to a relatively low state of cure in order to substantially non-resilient and responsive to the application to locally applied pressure. The required low degree of cure is obtained by use of a small amount of curing ingredients and by effecting curing under ambient air conditions simultaneously with the air drying operations described above.

Foam stabilization can be obtained by modification of the pH with ammonia, caustic potash, caustic soda, amines or the like; by use of protective colloids such as casein, glue, gelatin and the like or by use of surfactants, anionic dispersing agents such as the sodium salts of polymerized alkyl naphthalene sulfonic acid, soaps such as potassium stearate, potassium oleate and the like. Generally the foam stabilizer is incorporated in. amounts rangingfrom about 0.5 to about 1.25 parts per hundred parts of latex.

The curing ingredients employed in the present invention are generally a combination of both a vulcanizing agent and an organic cure accelerator. In accordance with the present invention, it is considered preferable that the foam be cured to a relatively low state of cure, thus the vulcanizing agent is admixed in relatively small amounts ranging from about 0.25 to about 2 parts per hundred parts of latex. Typical vulcanizing agents are for example sulfur, sulfur monochloride, thiuram disulfides, polysulfide polymers, alkyl phenol sulfides and the like. Sulfur is generally preferredas it is most economical. Typical organic accelerators are benzothiazyl disulfide, 2-mercaptobenzothiazole, tetraethylthiuram disulfide, tetramethylthiur'am disulfide, zinc dibutyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate and the like. The accelerators are employed in amounts ranging from about 0.25 to about 2 parts per hundred parts latex. This amount of curing ingredients together with curing under ambient air conditions has been found to impart sufficient rigidity to the cup-shaped pads to enable them to be handled while simultaneously not imparting resiliency to the foam.

Typical antioxidants which can be employed in the latex composition of the present invention are for example alkylated diphenylamines, hydroquinone monobenzyl ether, polybutylated bis phenol A, polymerized trimethyl dihydroquinoline, phenyl-B-naphthylamine and the like. Generally, from about 1 to about 3 parts of antioxidant per hundred parts of latex are employed.

In order to obtain the memory characteristic or high compression set of the foam cups of the present invention, it has been found necessary to add a tackifying resin to the latex composition. Typical tackifying resins are rosin derivatives such as hydrogenated rosin or rosin esters obtained by reacting the rosin acids with glycerol, pentaerythritol or other polyols and the like. Generally elastomeric resins such as natural rubber, polyisoprene, polybutadiene, SBR and the like can also be employed as tackifying resins. Preferably, Resin Emulsion No. 16, a modified rosin ester, prepared by General Latex and Chemical Corporation, Cambridge, Massachusetts is employed. Generally, from about 1.5 to about parts tackifying resin per hundred parts latex is sufficient to impart the desired memory effect or high compression set to the resulting foam.

Other additives can be employed if desired, for example, dyes and/or pigments can be admixed with the latex composition to impart color thereto, reodorants can be added to mask, for example, the typical rubber odor. Also, if desired, fillers such as clay, cork, talc and the like can be added. Moreover, a color fast dyed cotton floc can be added as both filler and colorant.

The cure activators employed in the present invention can be either organic or inorganic compounds. Most cure activators require zinc oxide and preferably both zinc oxide and a fatty acid in order to develop the best quality in the compound. Hence, it is considered preferable to add zinc oxide to the latex composition and most preferably to add both zinc oxide and fatty acid such as stearic acid thereto. Other activators which can be similarly employed include such materials as litharge, magnesium oxide, amines, amine soaps and the like. Generally, the cure activator is employed in amounts ranging from about 0.25 to about 2 parts per hundred parts latex.

The gelling agents which are employed to set or gel the latex foam are generally siliceous in nature and include silica, sodium silicofluoride and the like. Most preferably, sodium silicofluoride is employed. Generally, the gelling agent is employed in amounts ranging from about 2 to about 5 parts per hundred parts latex as required.

In one embodiment of the present invention the latex together with the foam stabilizer, the vulcanizing agent, the accelerator, the reodorant, an antioxidant, coloring agents and a tackifying resin are all charged simultaneously to a high speed mixer. The latex foam is then produced by beating air into the latex in a manner similar to that employed when making whipped cream. The volume of the latex must be increased at least about 10 times in order to obtain the desired foam density. Variations in the volume increase of the foam can be employed to alter the foam density. As the volume increases, the density of the foam decreases. After the foam has been beatened to the desired volume increase, the necessary cure activator and the gelling agent are added and dispersed throughout the mass. After the dispersing of these ingredients has been completed, the latex can be poured with relative ease. The workable time of the foam is dependent upon the amount of gelling agent and the prevailing room temperature. The working period can be adjusted from about 5 to about 10 minutes by proper control of these parameters, but use of the fastest practical gelling time is generally desirable in order to obtain the best foam properties. Generally, the foam is thereafter poured into cup-shaped molds which are then kept in order to maintain the desired shape. The foam is allowed to set and is then removed from the molds and air dried for about 36 to 48 hours to effect the necessary low degree of cure. Thereafter, any flashing can be removed. The foamed cups thus obtained exhibit low density and an excellent memory characteristic which is responsive to the local application of forces. The density of the foams produced as described above generally range from about 3 to about 5 lbs/ftf. It is considered necessary that the foam cups of the present invention be of low density in order to relieve the pressure on the distal end of the body member. Use of a high density foam could result in inflammation and ulceration of the distal portion of the body member and extreme discomfort and pain to the user. The foam cups of the present invention enable a total contact socket between the body member and the prosthetic device to be obtained. Total contact is necessary in order to activate the nerve endings of the body member to give the user the sensation of continuity with the prosthetic device.

Beating air into the latex is conveniently accomplished with mixers of the planetary rotation type using multi-wire whips and round bottom containers. The Hobart Mixers made by the Hobart Manufacturing Company of Troy, Ohio are illustrative of suitable mixers.

[t has been found that the amount of cure activator and gelling agent required will vary depending upon a number of factors, including ambient temperature, degree of beating, type of beater, and to some degree with the particular latex employed. It has been found that under warm ambient air conditions, the minimum amount of gelling agent should be employed; whereas, under cool air conditions, a larger amount will be required. The amount of gelling agent required can be readily determined by observing the length of time elapsing between the addition of the gelling agent to the mixer and the start of gellation. This time can be lengthened by using less gelling agent or shortened by increasing the amount thereof. However, it has been found that the gelling agent should not be employed in amounts below 2.0 wet parts to avoid excessive weakening of the internal structure of the foam.

Once the foam has been fully prepared, it will resemble whipped cream in appearance and can then be poured into the molds as set forth hereinabove. Aluminum molds are preferred and care should be exercised to obtain an alloy of aluminum which contains no copper or manganese as these two elements can interact with elastomeric latices to seriously reduce the aging resistance thereof. Adhesion to the metal molds may be minimized by use of a mold lubricant. It has been found that from about 10 to about 20 percent aqueous or isopropanol solutions of such materials as Carbowax 4000 manufactured by Union Carbide or Nopcolub manufactured by Nopco Chemicals have been found to be effective mold lubricants. After application of the lubricant to the mold, the lubricant must be allowed to dry on the mold before the foam is poured.

Gellation generally takes place in the foam structure within 5 to 10 minutes after the gelling agent is added. The time depends principally upon room temperature and the amount of the gelling agent employed. The foam at this stage, although solid, is easily deformed and care must be employed in the handling thereof.

Thus, the present invention provides a low density, nonresilient, deformable cushioning material exhibiting a memory characteristic for enhancing the cushioning effect of the interface between a body member and a prosthetic device, while providing a convenient means of altering the interior surface of the prosthetic device to enable total contact of the body member with the socket of the prosthetic device to be comfortably obtained. Thus, the interfacial member of the present invention, because of its memory characteristics and coloration, is adapted to provide a clear indication of the existence of pressure points which may arise between the body member and the prosthetic device. Accordingly, corresponding adjustments can be made to the prosthetic device thereby substantially alleviating discomfort due to bony prominences in the body member.

Although specific embodiments of the present invention have been illustrated and described, it is understood that various modifications thereof may be made Without departing from the spirit of the invention and the scope of the appended claims.

What is claimed is:

l. A diagnostic and interface pad adapted to be inserted between the socket of a prosthetic device and a body member to be fitted thereto for indicating the location of pressure points between the body member and device and for effecting a comfort interface therebetween consisting of a one piece relatively low density, substantially non-resilient, deformable polymeric foam pad exhibiting a cushioning characteristic, said foam including a tackifying resin which provides a memory for the pad characterized by a localized high compression set of the foam pad in response to locally applied forces and which set remains upon removal of the locally applied forces.

2. The interface pad of claim 1 wherein said pad is formed of a polymeric foam material having a relatively low cure.

3. An interface pad as defined in claim 2 comprising a removable insert for a prosthetic device.

4. An interface pad as defined in claim 2 laminated to the surface of the socket wall of the prosthetic device.

5. An interface pad as defined in claim 2 further including a colorant for imparting coloration to said pad, said coloration adapted to vary under application of locally applied forces thereby indicating the position of the local forces which are applied to said pad.

6. An interface pad as defined in claim 2 wherein said foam is a polymeric latex foam.

7. An interface pad as defined in claim 6 wherein said foam is a natural rubber latex foam.

8. In combination with a prosthetic device having a socket therein adapted to receive a human body member, a diagnostic and comfort interface pad comprising a cup-shaped body of polymeric foam situated upon the forward wall of said socket in the direction of movement, said pad comprising a relatively low density, substantially non-resilient, deformable, low-cured polymeric foam and a tackifying resin which causes said pad to exhibit a memory characterized by a localized set of said foam in response to locally applied forces and which set remains upon removal of the locally applied forces. 

1. A diagnostic and interface pad adapted to be inserted between the socket of a prosthetic device and a body member to be fitted thereto for indicating the location of pressure points between the body member and device and for effecting a comfort interface therebetween consisting of a one piece relatively low density, substantially non-resilient, deformable polymeric foam pad exhibiting a cushioning characteristic, said foam including a tackifying resin which provides a memory for the pad characterized by a localized high compression set of the foam pad in response to locally applied forces and which set remains upon removal of the locally applied forces.
 2. The interface pad of claim 1 wherein said pad is formed Of a polymeric foam material having a relatively low cure.
 3. An interface pad as defined in claim 2 comprising a removable insert for a prosthetic device.
 4. An interface pad as defined in claim 2 laminated to the surface of the socket wall of the prosthetic device.
 5. An interface pad as defined in claim 2 further including a colorant for imparting coloration to said pad, said coloration adapted to vary under application of locally applied forces thereby indicating the position of the local forces which are applied to said pad.
 6. An interface pad as defined in claim 2 wherein said foam is a polymeric latex foam.
 7. An interface pad as defined in claim 6 wherein said foam is a natural rubber latex foam.
 8. In combination with a prosthetic device having a socket therein adapted to receive a human body member, a diagnostic and comfort interface pad comprising a cup-shaped body of polymeric foam situated upon the forward wall of said socket in the direction of movement, said pad comprising a relatively low density, substantially non-resilient, deformable, low-cured polymeric foam and a tackifying resin which causes said pad to exhibit a memory characterized by a localized set of said foam in response to locally applied forces and which set remains upon removal of the locally applied forces. 